How were you working as a 2nd, 3rd, and 4th engineer? I assume you are working in these postitions in name only. On what types of vessels?
In order to get the RFPEW you need a USCG LICENSED 2nd Engineer Unlimited or a Chief Engineer Limited to sign off on the huge packet of assessments. They can't just be called the Chief or 2nd Engineer, they need the license. I think there are around 60 of the assessments. Plus you will need everything else that is involved. The USCG should have a checklist for RFPEW on their website.
I believe the vessel needs to be over 1,000hp and a few other requirements. Also, if you didn't serve onboard a steam powered vessel, you will not get the steam propulsion assessments signed off.
I don't believe there is a shortcut to getting the RFPEW. You either do the assessments or you don't get it. Good luck and tell us a bit more about why the USCG is denying your application. What exactly did you send them, what exactly did the say to you, etc.